Control of the Fixed Charge Distribution in an Ion-Exchange Membrane via Diffusion and the Reaction Rate of the Monomer

Abstract

The fixed charge distribution of the ion-exchange membranes was controlled by introducing ion-exchangeable groups onto the glycidyl methacrylate (GMA)-g-polypropylene (PP) membranes. The membranes were prepared by plasma-induced graft polymerization with uniform or nonuniform graft distributions over the cross section. The effects of reaction conditions on the graft distribution in plasma-induced graft polymerization were investigated to obtain the GMA-g-PP membranes with different graft distributions. The examined reaction conditions were plasma power, gas pressure of the plasma, solvent, concentration of the monomer solution, and reaction temperature. The graft distribution of the membranes was directly observed by a microscopic Fourier transform infrared mapping method and field-emission scanning electron microscopy. Also, the graft distribution was correlated with the relative magnitude of the reaction rate to the diffusion rate, which may determine the grafting yield as a function of the distance from the surface. A high rate of diffusion compared to the reaction rate resulted in a more uniform graft distribution. Among the grafting conditions, control of the reaction temperature was found to be the most effective for selectively preparing both uniform and nonuniform graft distribution. Uniform graft distribution was achieved when the reaction was conducted at 1 degrees C because of the relatively rapid diffusion and the slow reaction of the monomer, while nonuniform graft distribution occurred at higher reaction temperatures. Consequently, uniformly and nonuniformly charged cation-exchange membranes were prepared through sulfonation of the corresponding GMA-g-PP membranes at temperatures of 1 and 40 degrees C, respectively.

Recent Development of Polymer Electrolyte Membranes for Fuel Cells

“…Many researchers are interested in hydrocarbon polymers with an aliphatic main chain for PEMs. However, this kind of PEM is mainly used for low-temperature PEMFC or DMFC due to the inferior oxidative stability of these aliphatic main-chain hydrocarbon polymers. − The frequently used aliphatic main-chain hydrocarbon polymers include varieties of styrene-based block copolymers, CS, poly­(vinyl alcohol) (PVA), and so on. To enhance mechanical strength, methanol barrier, or proton conductivity, these polymers often require doping with inorganic proton-conducting moieties, blending with polymer pairs, or forming into IPNs.…”

Ionic Transport Properties of Cation-Exchange Membranes Prepared from Poly(vinyl alcohol-b-sodium Styrene Sulfonate)

“…Furthermore, the cost of manufacturing CEMs is relatively high. Therefore, many novel CEMs have been developed recently to overcome these problems [ 20 , 21 , 22 ]. These CEMs offer better control over the distribution of the fixed charges, and exhibit similar performance to conventional cation-exchange membranes.…”

Surface Modification by Graft Polymerization

“…Among the grafting conditions, control of the reaction temperature was found to be the most effective for selectively preparing the membrane with uniform or non-uniform graft distribution. (Choi et al, 2007). Uniform graft distribution was achieved when the reaction was conducted at 1 • C because of the relatively rapid diffusion and the slow reaction of the monomer, while non-uniform graft distribution occurred at higher reaction temperatures.…”

“…Yamaguchi et al (1996) found that the location of grafted polymer depended on the balance between the diffusivity and reactivity of monomers. Choi et al (2007) investigated the effects of reaction conditions on the graft distribution by examining plasma-induced graft polymerization in detail. Thus the grafted membrane morphology could be controlled by varying the monomer solvent.…”